THE NATION; New Ideas Are Changing Nuclear Debate

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A NEW generation of nuclear power plants - smaller, simpler and probably safer - is taking shape on the drawing boards. But rethinking the nuclear reactor is raising difficult issues for manufacturers and critics alike.

The conundrums involve safety. While the manufacturers can speak of marked improvements, they are reluctant to draw comparisons that would cast doubt on the safety of the 110 existing reactors, which have decades of service remaining.

The critics say the new designs sometimes trade old problems for new ones. Their latest study, which examines three distinct reactor systems, suggests that these designs are not without risks.

For years, the industry has asserted that its reactors are safe and pose only a minuscule chance of accident. Debates over what could be done to lower the risk further, industry officials say, are really debates over how safe is safe enough.

The issue has lost some of its edge lately, since all the plants ordered after 1974 in this country have been canceled and only a few are still under construction. But major reactor manufacturers sense the prospect of new orders, which would rekindle the debate.

The demand for power today is growing, and the fear of global warming gives nuclear generators an edge over those fired by coal, which releases carbon dioxide, a gas which scientists say tends hold heat in the atmosphere, contributing to global warming. Environmentalists have yet to embrace this logic, but it has encouraged the manufacturers, with large Federal subsidies, to invest hundreds of millions of dollars in drawing up new designs.

The new plants, like those already in service, would all split atoms to make heat, which is then used to make electricity, but they differ greatly in their approach. Yet all seek to use basic physical principles to increase safety. Incorporation of such principles, specifically the propensity of water to flow downhill and natural convection to limit overheating of small objects, can make a reactor ''inherently safe,'' according to the new design proponents.

One of the more promising designs is a gas-cooled graphite reactor proffered by General Atomics, a company based in San Diego, Calif., and one the Department of Energy would like to test. Heat-resistant graphite would encapsulate uranium fuel, and helium would conduct the heat needed to make electricity. Current reactors use fuel wrapped in metal, which melts at high temperature, and water, which transfers heat but can boil away in an accident. Helium's safety advantage over water lies in its already being a gas; in an accident water will turn to gas, thus losing much of its ability to carry away heat.

Risk Is Always Present

''The temperature characteristics of the fuel, and the inherent character of the helium, factors that are there because they are parts of physics, give you the inherent safety you're looking for,'' said Linden S. Blue, the vice chairman of General Atomics. The uranium cannot get hot enough to break out of its graphite shell, he said.

The General Electric Company is so persuaded of the significance of the new designs, not to mention the public-relations value of the phrase, that it has incorporated the term ''inherently safe'' into the name of one of its designs, the Power Reactor Inherently Safe Module, known as Prism.

But a study of three major reactor designs released last week by the Union of Concerned Scientists in Cambridge, Mass., which is regarded as the most technically competent of the private nuclear safety groups, said that such claims confuse the issue. According to Gregory C. Minor, a former manager in the advanced control and instrumentation department at General Electric and a consulting engineer who oversaw the study, ''You are dealing with a radioactive reaction, with enormous energy, and enormous potential disruptive action if you don't treat it properly.'' A reactor, he said, can no more be inherently safe than a car can be; improvements can be made, but risk is always present.

A few industry engineers privately concede the point. At the American Nuclear Energy Council, a lobbying group in Washington, James McDonald, a spokesman, said of the idea of inherent safety, ''I don't think that message has credibility.''

Another aspect of the newly proposed designs is their apparent lowering of defenses. Mr. Minor's firm, MHB Technical Associates, of San Jose, Calif., faulted some for lacking two secondary defenses: a containment building, the huge, costly concrete and steel structure devised to retain radiation accidentally released, and off-site emergency plans, which were required by the Nuclear Regulatory Commission after the accident at Three Mile Island, near Harrisburg, Pa., in 1979.

''There's nothing to contain,'' Mr. Blue argued, referring to the desirability of containment structures. ''It's about as useless as wearing a fur coat in the middle of summer.'' At Westinghouse, Richard J. Slember, the vice president and general manager of the Energy Systems Business Unit, said, ''It's a question of the need for an evacuation zone. That doesn't mean you wouldn't put that in. But the plant is so safe it may not require one.'' Before any new reactor could be built, the design would have to be approved by the Nuclear Regulatory Commission.

The Union of Concerned Scientists study, which analyzed the designs of General Electric, Westinghouse and General Atomics, welcomed some of the innovations. It applauded taking advantage of natural features in accomplishing vital tasks, including removing heat that continues to be produced after the nuclear reaction has ceased, also known as radioactive decay, which can cause a meltdown.

The study found some countervailing disadvantages. In two designs, ''the passive-decay, heat-removal systems which appear to be so beneficial in terms of accident prevention appear also to present a significant potential sabotage vulnerability,'' the study said, because the heat outlets are above ground. In existing reactors, heat is generally dissipated through cooling towers or into rivers and oceans.

Another design change is to build far smaller reactors, so that the amount of heat that must be removed in an accident is small enough to be removed by natural convection or other simple systems. One design calls for nine clustered reactors, run from a single control room with four operators. Yet mistakes have already occurred with operators at two-reactor control rooms, the study said.

Even as the study was being released, the American Nuclear Energy Council responded that the criticism was premature ''because of the rapidly evolving aspects of these designs.'' The Union of Concerned Scientists, it said, was showing ''its bias against nuclear energy and its long-held goal of phasing out nuclear energy plants.''

Mr. Minor, who oversaw the study for the Union of Concerned Scientists, said that even with looming questions about safety, new reactors might be ordered later in this decade. But unless the issues are resolved, he said, the second generation will be few in number and short lived.

A version of this article appears in print on July 22, 1990, on Page 4004005 of the National edition with the headline: THE NATION; New Ideas Are Changing Nuclear Debate. Order Reprints|Today's Paper|Subscribe